Internal combustion engines (or simply referred to as engines) are commonly applied as prime movers in a variety of applications and environments. Over the years, numerous attempts have been made to reduce emissions and to improve efficiency of such engines. For example, engine manufacturers and operators have proposed the need to combust leaner air-fuel mixtures for improving efficiency and use exhaust gas recirculation (EGR) to reduce emissions such as of Nitrogen Oxides (NOx).
In some situations, engines may apply high EGR and/or relatively leaner air-fuel mixtures. However, in such situations, conventional ignition systems associated with such engines may find it difficult to provide a stable, consistent combustion of the air-fuel mixture. For effective combustion in such situations, engines are required to have suitable provisions that facilitate adequate ignition. However, several of the currently available engines lack such provisions, and the engines that do, may incorporate encapsulated spark plugs or pre-chamber engine designs, with or without fuel enrichment or purging. Such provisions may help achieve a more robust and consistent ignition phenomenon, but the use of such provisions may require additional NOx treatment and extensive service. Further, some ignition strategies include the use of fuels, such as diesel, for providing a pilot ignition, but use of such strategies may produce particulate matter and soot, affecting engine emissions.
U.S. Pat. No. 7,464,688 ('688 reference) relates to an internal combustion engine that has compression temperatures and pressures that do not support auto-ignition of a fuel-air mixture. Ignition is achieved by injecting active radicals into the air-fuel mixture. The '688 reference also discloses that the active radicals are provided by withdrawing a portion of the air-fuel mixture, treating it to produce active radicals in the portion and returning the portion to the air-fuel mixture. Treatment of the portion typically includes simultaneously injecting, mixing, and compression of a predetermined amount of pilot fuel within the portion.